Mapping Migrations Essay, Research Paper

Sometime this winter, waterfowl experts from across Canada will gather for their

annual "wing bee." Their task will be to sort through a small mountain

of duck wings obtained from a randomly selected group of hunters, and assign the

wings to piles by species, age and sex. Together with statistics from similar

shindigs held in the United States, this information will provide a picture of

the year’s kill and will also offer hints about the ups and downs of duck

populations. That may seem like a lot to learn from a heap of dried-up remains

but, to Len Wassenaar of the National Water Research Institute in Saskatoon, a

room full of duck wings is like an archive that can be studied for clues about

each bird’s life history and movements. Wassenaar and his colleague Keith Hobson

of the Canadian Wildlife Service have developed a technique for reading a

feather’s chemistry and tracing it onto a map. The story begins with rain, which

always contains a minute percentage of heavy water. That’s regular H2O burdened

with deuterium, a rare isotope of hydrogen. In North America, the amount of

deuterium in rainfall is greatest along the Paci?c coast and decreases to the

east and south, as weather systems sweep across the continent. Every region has

a unique "hydrogen isotope signature" – a characteristic ratio of

ordinary hydrogen to deuterium – imprinted onto the ecosystem, passing from the

rain into soil, soil into plants, plants into birds and animals. When the

hydrogen is incorporated into hard tissues, it provides a lasting clue to where

those tissues were made. Last year, Wassenaar and Hobson used this fact to

resolve a mystery that has troubled researchers for decades. Since the

mid-1970s, we’ve known that monarch butterflies congregate for the winter in a

dozen remote locations in central Mexico. Several hundred million monarchs from

Eastern Canada and the U.S. settle onto the hillsides in orange drifts. But once

the insects have landed, they all look the same to us, and we have no way of

knowing their precise origins. Which ones came from Ontario? Which from Ohio? If

one of the wintering sites were logged, how would this affect the breeding

stock? The tried-and-true technique of tagging, which has taught us so much

about the migratory movement of birds, has been disappointing with monarch

migration. Over the past 50 years, hundreds of thousands have been marked with

tiny identi?cation stickers, yet fewer than 130 have ever been recovered in

Mexico. "The tag recoveries are really appalling," Wassenaar laments.

The beauty of the new technique is its directness. By gathering dead butterflies

from the wintering sites and analyzing them in the lab, Wassenaar and Hobson

were able to read each individual’s hydrogen signature. This in turn revealed

where the butterflies had grown up. As a result, we now know that the monarchs

at the winter roosts are of mixed origins (Ontarians and Ohioans crammed in wing

by wing) and that most of the overwintering flocks come from the midwestern U.S.

The discovery of the midwest’s crucial importance in maintaining the breeding

stock will provide an added focus for conservationists. Gratified by this

success, Wassenaar purrs with confidence. "The sky’s the limit with this

new tool," he says. Rather than spend years on banding projects, with

uncertain results, why not head for the isotope lab and an immediate outcome?

Certainly, that prospect appeals to Bob Clark, also of the CWS, who has urgent

concerns about the welfare of the lesser scaup, a diving duck. (That’s "scawp,"

an imitation of the bird’s characteristic squawk.) Cute as a rubber ducky with

its upturned blue bill, the scaup has traditionally been among the most

plentiful of waterfowl, with an estimated population of six million. But its

numbers took a downturn in the mid-1980s, a trend that has recently intensified

into a seven-year sequence of record lows. Two-and-a-half million birds have

vanished. The losses seem to be worst for scaups that nest in the boreal forest

of northern Alberta and the southwest Northwest Territories. Is "something

funny going on" in the north woods, as Clark suspects, or does the source

of the problem lie farther south, along the birds’ migration route or on their

wintering grounds in Mexico and the U.S.? These perplexities would be easier to

cope with if we knew precisely where scaups from the boreal forest go for the

winter. Clark thinks the answers may lie in the scaup wings that are submitted

for the annual bees. Scaups grow new feathers before leaving their breeding

range, so their hydrogen signature should tell him where each bird spent the

summer, be it on the plains or in the forest. By mapping this location and the

spot where the duck was shot, he expects to build a detailed picture of scaup

migrations and wintering grounds. Similar information is required for a growing

number of migratory species, including many of our favourite songbirds. Since

population declines tend to affect particular subpopulations (like the boreal

forest scaup), we can no longer get by with a broad-brush sketch of migratory

movements. The hydrogen-isotope technology offers to fill in the details at a

moment when this knowledge is urgently needed. Candace Savage is a

Saskatoon-based writer and author of 18 books on wildlife, environmental issues

and other subjects.